Impact assessment following an oil spill near Yorkeys Knob, north Queensland

Brief description

Surface sediments were collected in January 1994, after oil was dumped along a road adjacent to sugar cane fields and wetlands near Yorkys Knob, north Queensland. Samples were taken from a variety of visually oiled and unoiled wetland areas, the oiled road, and the stock pile of oiled sediments that had been scraped off the road during initial clean up efforts.Core samples were also collected using a hand coring device, made from 4 cm diameter aluminium pipe. Cores were taken by pounding the tube into the sediment and twisting it back up to the surface. Cores were removed, sliced with a steel knife and samples were taken from the centre of specific depth layers (0-2, 10-12, 16-18, 25-27 and 38-40 cm) and put into labelled jars. The soil samples were packed on ice and taken to a commercial laboratory in Cairns, which sent the samples to their Melbourne laboratory for analysis of total hydrocarbons by gas chromatography with flame ionisation detection (GC-FID).After evaluation of the first set of chemical data, three sites were selected for longer term impact assessment. Site 3 was in a Melaleuca forest and samples were collected in three areas: heavily oiled, 5 m from the road (3A); moderately oiled at 15 m from the road (3B); and unoiled at 30 m from the road (3C). Site 6 was located 5 m from the road in dense intertidal mangrove forest composed predominantly of Avicennia marina. Site 5 was a small tributary, which drained the most heavily oiled wetlands and flowed into Richters Creek. Sampling at these sites was conducted in January and June 1994, May and July 1995 and the samples sent to the commercial laboratory for analysis. The final samples were collected in December 1995 and were analysed at AIMS for individual components. Oil composition was determined by three independent methods of analysis: (1) scanning ultraviolet fluorescence (UVF), (2) GC-FID, and (3) Selected IonMonitoring GC/Mass Spectroscopy (GC/MS) for individual aromatic hydrocarbons and triterpane biomarkers.QDEH also sank 25 cm diameter aluminium tubes into the sediment at 5 monitoring sites, to a depth of around 3 m, to determine if oil was leaching from the contaminated sediments into ground water. Sampling was done with a stainless steel tube, after each bore was cleared of water and allowed to refill. Water was collected and 500 ml drained into 1 litre glass jars to ensure that no oil from previous accumulations of surface water contaminated the ground water samples. The samples were placed on ice and airfreighted along with the sediments for analysis.Additional sampling was done in May 1995 at six sites along the roads in the sugar cane farm. These sites were excavated with a shovel and each layer was examined for visual and olfactory presence of oil. Samples for chemical analysis were taken in layers likely to contain oil, if it had seeped through the road into subsurface layers, such as into clays at ground water level. These samples were analysed at AIMS. An estimated 76,000 litres of a mixture of fuel and lubricating oils were dumped on a road, adjacent to sugar cane fields near Yorkys Knob, north Queensland in January 1994. The oil soaked into sediment and contaminated a band along the road 30m wide and 200m long. Mangroves and a Melaleuca forest were impacted.AIMS was contracted by the Queensland Department of Environment and Heritage (QDEH) to assist in producing an impact assessment. The specific tasks undertaken were:1. supervision and participation in sediment sampling2. an assessment of the analytical methods used by the contracting commercial laboratory3. interpretation of the analytical data in terms of oil composition, its probable toxicity, and the rate and patterns of dispersion and degradation of the contaminant hydrocarbons4. detailed chemical analysis of initial and final samples5. comparison of the results with data obtained from long term impact assessments of oil spills in other tropical wetlands. At the time that the dumping occurred, the surface oiling of powdery dirt roads in sugar cane fields had been practiced for about 20 years in Queensland.

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Maintenance and Update Frequency: notPlanned

Statement: Statement: The sampling methods used were the same as those used in other successful assessment studies of oil spills in mangroves (Keller and Jackson, 1993).The following analytical protocol was used by the commercial laboratory.Total petroleum hydrocarbons in sediments were determined by defrosting and homogenising samples, weighing out a 20 g subsample of wet sediment into a glass flask, adding 50 ml of (distilled-in-glass grade) methylene chloride to the flask, sample extraction assisted by sonication and removal of 1 ml of the extract into a vial for analysis by flame ionisation gas chromatography (GC). The method is based on US EPA Methods 3510, 3550 and 8000. The method generally follows the guidelines for the "Determination of Petroleum Hydrocarbons in Sediments" as published by UNEP/IOC/IAEA (1992); without any sample drying or extract concentration steps. The laboratory followed quality control procedures which included: 1) 5 % of samples were reagent/analytical blanks, 2) Standards extending throughout the expected range of results were run at the beginning and during each set of analyses, 3) A sample was analysed in duplicate at least once every 20 samples or once for each separate job, 4) Surrogate standard recoveries were performed at least once in every 20 samples or once for each job and 5) Whenever available, control samples were run with each set of samples. Dry weights were calculated by drying a separate sub sample. This procedure involves no solvent concentration or sample clean up step. Results are reported over specific n-alkane elution ranges with the following detection limits: C6-C9 and C10-C14: 20 mg/kg, C15-C28: 50 mg/kg and C29-C36: 100 mg/kg. All results are reported in mg/kg dry wt. The reported totals are the sum of resolved and unresolved components within these elution ranges. Water samples were also solvent extracted and analysed by GC. Results were reported with the following detection limits: C6-C9 and C10-C14: 0.2 mg/l, C15-C28: 0.5 mg/l, and C29-C36: 1.0 mg/l.Interpretation of the types of oil in samples and the compositional changes due to weathering processes was based on the pattern of hydrocarbons as observed in the gas chromatograms. The principles of this interpretation were detailed in UNEP/IOC/IAEA (1992) and have evolved from numerous published oil spill assessment studies. The most relevant comparison for assessment of oil in mangrove ecosystems, comes from the Long Term Assessment of the Bahia las Minas (Panama) Oil Spill (Keller and Jackson, 1993).The analytical methods used at AIMS are described in detail in UNEP/IOC/IAEA (1992) and discussed by Burns (1993). The methods consist of exhaustive solvent extraction with CH2Cl2 followed by rotary and N2 evaporation steps and an adsorption chromatography clean-up procedure using alumina. Burns KA (1993). Analytical methods used in oil spill studies. Marine Pollution Bulletin 26: 68-72.Keller B and Jackson JBC (eds) (1993) Long term assessment of the oil spill at Bahia las Minas, Panama. Synthesis Report. U.S. Minerals Management Service. OCS 93-0048.UNEP/IOC/IAEA (1992) Determination of petroleum hydrocarbons in marine sediments. IOC Manual and Guides No. 20 Rev. 1, 75 pg. Prepared by KA Burns.

Notes

Credit
Burns, Kathryn A, Dr (Principal Investigator)